In the present 3GPP (Third Generation Partnership Project) protocol, when handover procedure is implemented by MME (Mobility Management Entity), and any process irrelevant to Handover such as bearer activation/modification/deactivation, Location reporting control or NAS message transfer (Non Access Stratum message transfer), etc. occurs, MME needs to delay these processes and implement them until handover procedure is completed, or these processes are deemed to have failed.
This is described in TS 23.401: